There is a need to reduce the operating costs of a storage system that comprises multiple storage apparatuses (for example, a data center). Technology like the following has been disclosed for this type storage system.
Patent Literature 1 relates to technology called “storage virtualization”. In this specification, a storage apparatus that comprises a storage virtualization function will be called a “virtual storage”. Furthermore, in this specification, a storage apparatus, which is coupled to the virtual storage and comprises a storage resource that is virtualized in accordance with the virtual storage, will be called an “external storage”. In the Patent Literature 1, one or more external storages are coupled to one virtual storage, and for all appearances the external storage is concealed by the virtual storage. In this specification, a logical volume, which is the access unit of a server or other such host apparatus, will be called a “LU” (LU: Logical Unit). A LU, which is mapped on a one-to-one basis to a LU on the virtual storage, is defined on the external storage. Hereinbelow, a LU, which is accessed from the server, will be called a “server LU”, and a LU on the external storage will be called an “external LU”. In a case where the virtual storage receives from the host apparatus an access request that specifies a server LU mapped to the external LU, this access request is processed by accessing this external LU. This technology makes it possible to reduce management costs since an administrator only needs to manage the virtual storage.
Patent Literature 2 relates to technology called “capacity virtualization”. Capacity virtualization is also called thin provisioning (or dynamic provisioning). In this specification, the virtual storage also comprises a capacity virtualization function. The capacity virtualization function partitions a storage area called a “capacity pool” into segments called “pages”. Generally speaking, when a LU is defined, the capacity of this LU is also specified, and a storage area corresponding to this capacity is secured in the storage apparatus. Meanwhile, in the virtual storage that has the capacity virtualization function, there is no need to secure a storage area proportional to the capacity of a virtual server LU (a server LU that conforms to thin provisioning) at the time this virtual server LU is defined. In a case where a write is actually generated to the virtual server LU, a page is allocated to the area (an area in the virtual server LU) that comprises this write destination. This makes it possible to reduce the storage area that is consumed. Furthermore, since the generation of the write triggers the allocation of the storage area, the administrator only needs to define the appropriate virtual server LU capacity, thereby making it possible to reduce management costs.
Patent Literature 3 discloses a technology that applies a capacity virtualization function to a storage area of the external storage. Since this technology can only be applied once both technologies, i.e. “storage virtualization” and “capacity virtualization”, are present, it is considered to be important as a high value-added technology. In accordance with this, a large-capacity external LU, for example, is defined on the external storage. This external LU becomes one of the capacity pools on the virtual storage. The virtual storage partitions this capacity pool (the capacity pool mapped to the external LU) into multiple pages. In a case where a write is generated to the virtual server LU, the virtual storage allocates a page to the area comprising this write destination. In accordance with this, an internal page (a page in the capacity pool that is based on a physical storage device inside the virtual storage) and an external page (a page in the capacity pool mapped to the external LU) may be mixed together in the multiple pages that are allocated to the one virtual server LU.
The technologies disclosed in Patent Literatures 1 through 3 were applied in a case where the number of virtual storages was equal to or larger than one. However, linking multiple virtual storages together is also effective at further reducing operational management costs. For example, Patent Literature 4 discloses a technology for linking two virtual storages and backing up both storages. Furthermore, Patent Literature 4 also discloses a technology, which, in an environment in which multiple virtual storages share the external storage, migrates authority to access the external LU on the external storage from a certain virtual storage to a different virtual storage without copying the data of the relevant LU for the purpose of load leveling.